U.S. Pat. No. 6,113,874 discloses heat recovery methods useful with furnaces employing regenerators wherein a stream of combustion products formed in the furnace is passed through a first regenerator to heat the first regenerator and cool the combustion products, and then a portion of the cooled combustion products is combined with fuel to form a mixture which is passed through a second heated regenerator and where it undergoes an endothermic reaction to form syngas that then passes into the furnace and is combusted.
The present invention is an improvement in the methods disclosed in that patent, whereby it has unexpectedly been found that the efficient heat recovery afforded by these methods can be improved and other benefits described herein can be realized. In particular, the present invention enables the operator to obtain an adiabatic flame temperature that is higher than that of methane, thus making available the advantages that follow from having such a higher flame temperature. The aforementioned U.S. Pat. No. 6,113,874 does not teach how such a higher flame temperature can be attained in the thermochemical regeneration method described in that patent.
Flame temperature and available heat in a furnace are important properties of combustion of fuel and oxidant that influence the fuel consumption and the productivity of the furnace. Flame temperature of a fuel and an oxidant is typically defined as the thermodynamic equilibrium temperature of the combustion products without any heat loss to the surrounding and is known as adiabatic flame temperature. The actual flame temperature in an industrial furnace is significantly lower than the adiabatic flame temperature since heat is transferred from the flame to furnace charge and surrounding walls. However, an increased adiabatic flame temperature is directly correlated to an increased actual flame temperature that is realized in operation of a furnace such as furnaces with which the present invention can be practiced. Available heat of a fuel in a furnace is typically defined as the percent of the lower heating value (LHV) of the fuel available in the furnace for heat transfer to the furnace charge and the furnace walls and calculated as the difference of the furnace fuel input (LHV) and the sensible heat of flue gas exiting the furnace. In general higher flame temperature correlates with higher available heat for most fuel-oxidant systems. It is well known that both flame temperature and available heat increase substantially when oxygen is used in place of air for combustion. For example oxy-acetylene flame produces a very high temperature and is widely used for welding of metals. If acetylene is used as a fuel in place of natural gas in an industrial furnace such as a glass furnace, the fuel efficiency is improved substantially because of its high available heat. Due to the very high cost of acetylene, however, it is not considered as a practical fuel for industrial furnace applications. There is a need to improve the properties of common hydrocarbon fuels such as natural gas to increase the flame temperature and available heat for industrial furnace applications.